Cross groove type constant velocity joint

ABSTRACT

A constant velocity joint for a drive system includes: an outer joint member and an inner joint member, each having a plurality of ball grooves, the ball grooves consisting of a first group of grooves of a skewed groove shape with a first skew angle other than zero and alternately arranged in opposite directions relative to an axis of rotation of the outer and inner joint members, and a second group of grooves of a skewed groove shape with a second skew angle other than zero and alternately arranged in opposite directions relative to an axis of rotation of the outer and inner joint members, the second skew angle less than the first skew angle. In addition to the differentiated skew angles, the contact angles of the balls in the first and second group of grooves may also be differentiated.

REFERENCE TO RELATED APPLICATIONS

This is a divisional of U.S. patent application Ser. No. 12/582,602filed on Oct. 20, 2009, the entire contents of which are incorporatedherein by reference.

FIELD OF THE INVENTION

The present invention relates to a cross groove type constant velocityjoint for use in a drive system, and more particularly, to a crossgroove type constant velocity joint having composite groove shapes,typically for use in a drive system of, for example, an automobile fortransmitting rotational torque between two rotating shafts thereof.

BACKGROUND OF THE INVENTION

A cross groove type constant velocity joint (hereinafter to be referredas a “cross groove joint”) is one type of constant velocity universaljoints used for transmitting rotational torque between the rotatingshafts (i.e., the driving shaft and the driven shaft), typically for thedrive system of automobiles. The cross groove joint includes an outerjoint member with a plurality of ball grooves formed on the innersurface thereof, and an inner joint member with a plurality of ballgrooves formed on the outer surface thereof, in which the correspondingball grooves of the outer joint member and the inner joint member areconfigured to pair with each other and slanted with the same skew angleand in opposite directions with respect to the center or rotating axisof the joint.

FIGS. 1-2 illustrate one example of a conventional cross groove typejoint which retains six balls in the ball grooves for transmitting therotational torque between the outer and inner joint members to drive thedrive system. This cross groove joint includes an outer joint member 1with six grooves formed on the inner surface thereof, an inner jointmember 3 with six grooves formed on the outer surface thereof, six balls2 retained in the pared grooves of the outer and inner joint members fortorque transfer between the outer and inner joint members 1 and 3, and acage 4 configured to support the balls 2 to a plane bisecting the angleof articulation between the axes of rotation of the outer and innerjoint members 1 and 3.

In the structure of the conventional cross groove joint as shown in FIG.2, the outer joint member 1 has a plurality of (i.e., six) inwardlyfacing outer ball grooves 1 a alternately skewed with a skew angle δ inopposite directions relative to an axis of rotation of the outer jointmember 1. The inner joint member 3 positioned inside the outer jointmember 1 has a plurality of (i.e., six) outwardly facing inner ballgrooves 3 a alternately skewed with the same skew angle δ in oppositedirections relative to an axis of rotation of the inner joint member 3.The outer and inner ball grooves 1 a and 3 a face each other in crossedpairs with each of the balls 2 positioned between each crossed pair fortorque transfer between the inner and outer joint members 1 and 3. Asthe ball 2 is retained in the cage 4, the ball 2 is limited in a ballmovement range L2 in the circumferential direction of the joint, and theouter joint member 1 has a minimum thickness L1 on one side of themember. To secure the movement of the balls 2, the cage 4 includes aplurality of (i.e., six) cage windows 4 a with a dimension sufficient toaccommodate the ball movement L2. As a result, the width L4 of each cageweb 4 b must be designed to have a dimension at least the same or lessthan the minimum thickness L1 of outer joint member 1.

In an attempt to reduce a transmission error and to make the design ofthe joint more compact, the cross groove joints retaining eight ballshave been suggested. The eight-ball type cross groove joint known in theart typically has a basic structure generally the same or similar tothat shown in FIGS. 1-2, however, with the number of the balls and thenumber of the ball grooves of the outer and inner joint membersrespectively increased from six to eight. FIGS. 3( a) and (b) illustratea conventional cross groove joint with eight balls. Like the six ballcross groove joint, the eight ball cross groove joint includes an outerjoint member 11, an inner joint member 33, balls 22 for torque transferbetween the outer and inner joint members, and a cage 44 configured tosupport the balls to a plane bisecting the angle of articulation betweenthe axes of rotation of the outer and the inner joint member.

In the structure of the conventional eight ball type cross groove jointas shown in FIG. 4, the outer joint member 11 has a plurality ofinwardly facing outer ball grooves 11 a alternately skewed with a skewangle δ in opposite directions relative to an axis of rotation of theouter joint member. The inner joint member 33 placed inside the outerjoint member 11 similarly has a plurality of (i.e., eight) outwardlyfacing inner ball grooves 33 a alternately skewed with the same skewangle δ, however, oriented in opposite directions relative to an axis ofrotation of inner joint member 33. The outer and inner ball grooves 11 aand 33 a face each other in crossed pairs with each of the balls 22retained between each crossed pair for torque transfer between the innerand outer joint members. As the ball 22 is retained in the cage 44, theball 22 is limited in a ball movement range L22 in the circumferentialdirection of the joint, and the outer joint member 11 has a minimum(least) thickness L11 on one side of the member. To secure the movementof the balls 22, the cage 44 includes a plurality of (i.e., eight) cagewindows 44 a with a dimension sufficient to accommodate the ballmovement L22. As a result, the width L44 of each cage web 44 b must bedesigned to have a dimension the same or less than the minimum thicknessL11 of outer joint member 11.

As the cross groove joint with higher balls (e.g., eight or more balls)can provide more compact design and secure a smoother and reliableoperation as compared to the cross groove joint with six balls, it wouldbe desirable to produce a higher ball (e.g., eight or more balls) typecross groove joint which has the same or equivalent durability as thathaving six balls. More specifically, if the cross groove joint witheight balls, for example, is designed to have the same pitch circlediameter (PCD) as the joint having six balls, the ball diameter of theeight ball joint can be reduced because the load on each ball groove andthe stress onto the cage web 44 b decreases by the increase of thenumber of the balls. In addition, the size of each cage window 44 a canalso be reduced compared to the joint containing six balls.

However, the higher ball (e.g., eight ball) type cross groove joint mayalso include certain shortcomings or disadvantages as described below,for example. Because the eight ball type joint includes more (i.e.,eight) cage windows 44 a, the thickness of the cage web 44 b is alsoreduced, and thus, the stress on the cage web 44 b becomes greater thanthat of the six ball type. Comparing to the joint with six balls havingthe same PCD, the increased amount of stress on the cage web (due to thereduction of cage web thickness) exceeds that of the decreased amount ofstress owing to the increase of the number of balls. Therefore, thehigher ball (e.g., eight ball) type cross groove joint may have aweakened strength and durability in the cage web, and thus, the loadbearing capacity of the joint can be deteriorated than that of theconventional six ball type joint.

SUMMARY OF THE INVENTION

In order to solve the above described and other shortcomings ordrawbacks known in the conventional cross groove joints, the presentinvention provides a cross groove joint (preferably, but notnecessarily, of higher ball type) with a compact and durable structure,in particular, with the strength of the cage web enhanced than that ofthe conventional cross groove joints as described above.

In order to provide an enhanced strength to the cage web of the crossgroove joint, the present invention provides a cross groove jointincluding an outer joint member with a plurality of inwardly facing ballgrooves and an inner joint member with a plurality of outwardly facingball grooves, in which the shapes of the ball grooves of the outer andinner joint members are configured to increase the thickness and alsothe mechanical strength of the cage web as compared to the conventionalcross groove joint as described above.

The mechanical strength and durability of the cage is influenced by skewangle δ (see FIG. 4, for example). As the skew angle δ of the ballgrooves for the outer and inner joint members 11 and 33 increases, theball movement L22 in circumferential direction increases and the size ofcage window 44 a should also be increase to accommodate the ballmovement in the movement range. As a consequence, the thickness of cageweb 44 b between two adjacent windows 44 a becomes smaller as the skewangle of the grooves for the inner and outer joint member increases.Therefore, considering all the factors described above, the applicant ofthe present application discovered several effective ways to reduce theball movements and the size of cage windows in the cross groove joint(preferably, but not necessarily, of the type having eight or moreballs) by decreasing or optimizing the skew angle and also optimizingthe shapes of the ball grooves. U.S. patent application Ser. No.12/563,029, filed Sep. 18, 2009 by the same applicants of the presentapplication, suggests several examples of the constant velocity jointsincorporating composite groove patterns (for example, such as acombination of liner and non-linear grooves, or of skewed grooves andnon-linear grooves) to the ball grooves of the outer and inner jointmembers to provide an enhanced strength and durability comparing to theconventional cross groove type joint.

The present application provides a cross groove type constant velocityjoint having outer and inner joint members with different grooveconfigurations to the ball grooves of the outer and inner joint membersto provide an enhanced strength and durability comparing to theconventional cross groove type joint. According to one aspect of thepresent invention, the ball grooves of the outer and inner joint membersare configured to have two groups of skewed grooves composed of a firstgroup with a skew angle as same as or similar to the skew angle (δ) ofthe conventional groove type joint (as shown in FIG. 4 for example) anda second group with a reduced skew angle which is less than the skewangle (δ) of the conventional groove type joint. As a result, theminimum thickness (L11) of the outer and inner joint members and thethickness of the cage web can be enlarged relative to the conventionalgroove type joint having the alternately arranged skewed grooves of thesame skew angle (δ). Accordingly, the joint of the present invention canprovide an enhanced strength and durability over the conventional crossgroove type joint.

As described below in association with the eight ball type joint, forexample, in order for the eight ball cross groove joint to secure thestrength and durability of the cage to the level similar or equivalentto that of the six ball cross groove joint having the same pitch circlediameter (PCD), the skew angle is reduced and the minimum thickness(least effective thickness) of the outer and inner joint members (andthus, the thickness of the cage web as well) are maximized as comparedto the conventional joint described above without any degradation offunctions in the joint.

According to one preferred embodiment of the invention, a cross groovetype constant velocity joint for a drive system comprises:

an outer joint member having a plurality of inwardly facing outer ballgrooves, the outer ball grooves consisting of a first group of grooves,each groove of which having a skewed groove shape with a first skewangle other than zero and alternately arranged in opposite directionsrelative to an axis of rotation of outer joint member, and a secondgroup of grooves, each groove of which having a skewed groove shape witha second skew angle other than zero and alternately arranged in oppositedirections relative to an axis of rotation of outer joint member, thesecond skew angle less than the first skew angle;

an inner joint member disposed inside the outer joint member and havinga plurality of outwardly facing inner ball grooves consisting of a firstgroup of grooves, each groove of which having a skewed groove shape witha first skew angle other than zero and alternately arranged in oppositedirections relative to an axis of rotation of inner joint member, and asecond group of grooves, each groove of which having a skewed grooveshape with a second skew angle other than zero and alternately arrangedin opposite directions relative to an axis of rotation of inner jointmember, the second skew angle less than the first skew angle, each innerball groove of the inner joint member being coupled with a correspondingouter ball groove of the outer joint member generally in crossed pair;

a plurality of torque transfer balls which are guided by the ball groovefaces of the outer and inner joint members; and

a cage having circumferentially displaced windows to accommodate theballs therein.

According to another aspect of the present invention, the shapes andconfigurations of the outer and inner joint members (including the ballgrooves thereof) are further modified to provide an enhanced strengthand durability, while also capable of reducing frictions andtransmission errors in the joint causable by rotational backlash whenusing two groups of skewed grooves, one group with regular skew anglesand the other with reduced skew angles. In order to resolve thepotential risks of increasing the rotational backlash due to the reducedskew angle in the second group of grooves (which will be discussed belowin details), the applicants discovered that the rotational backlash canbe decreased as the contact angle between the ball and the ball groovefor the inner and outer joint members increases and as the skew angle ofthe ball grooves increases. The applicants further discovered that therotational backlash can also be decreased as the pitch circle diameter(PCD) increases. Based on these findings, the applicants furtherdiscovered several effective ways (as described below in details withreference to FIGS. 6-11) to reduce the rotational backlash in the ballgrooves, while also maintaining a similar or equivalent strength anddurability of the joint.

According to one preferred embodiment of the invention, a cross groovetype constant velocity joint for a drive system comprises:

an outer joint member having a plurality of inwardly facing outer ballgrooves, the outer ball grooves consisting of a first group of grooves,each groove of which having a skewed groove shape with a first skewangle other than zero and alternately arranged in opposite directionsrelative to an axis of rotation of outer joint member, and a secondgroup of grooves, each groove of which having a skewed groove shape witha second skew angle other than zero and alternately arranged in oppositedirections relative to an axis of rotation of outer joint member, thesecond skew angle less than the first skew angle;

an inner joint member disposed inside the outer joint member and havinga plurality of outwardly facing inner ball grooves consisting of a firstgroup of grooves, each groove of which having a skewed groove shape witha first skew angle other than zero and alternately arranged in oppositedirections relative to an axis of rotation of inner joint member, and asecond group of grooves, each groove of which having a skewed grooveshape with a second skew angle other than zero and alternately arrangedin opposite directions relative to an axis of rotation of inner jointmember, the second skew angle less than the first skew angle, each innerball groove of the inner joint member being coupled with a correspondingouter ball groove of the outer joint member generally in crossed pair;

a plurality of torque transfer balls which are guided by the ball groovefaces of the outer and inner joint members; and a cage havingcircumferentially displaced windows to accommodate the balls therein;

wherein the first group of grooves of the outer and inner joint membersare configured to have a first contact angle between its ball and ballgroove, respectively, and the second group of grooves of the outer andinner joint members are configured to have a second contact anglebetween its ball and ball groove, respectively, and wherein the secondcontact angle is selected to have an angle larger than the first contactangle.

According to another preferred embodiment of the invention, a crossgroove type constant velocity joint for a drive system comprises:

an outer joint member having a plurality of inwardly facing outer ballgrooves, the outer ball grooves consisting of a first group of grooves,each groove of which having a skewed groove shape with a first skewangle other than zero and alternately arranged in opposite directionsrelative to an axis of rotation of outer joint member, and a secondgroup of grooves, each groove of which having a skewed groove shape witha second skew angle other than zero and alternately arranged in oppositedirections relative to an axis of rotation of outer joint member, thesecond skew angle less than the first skew angle;

an inner joint member disposed inside the outer joint member and havinga plurality of outwardly facing inner ball grooves consisting of a firstgroup of grooves, each groove of which having a skewed groove shape witha first skew angle other than zero and alternately arranged in oppositedirections relative to an axis of rotation of inner joint member, and asecond group of grooves, each groove of which having a skewed grooveshape with a second skew angle other than zero and alternately arrangedin opposite directions relative to an axis of rotation of inner jointmember, the second skew angle less than the first skew angle, each innerball groove of the inner joint member being coupled with a correspondingouter ball groove of the outer joint member generally in crossed pair;

a plurality of torque transfer balls which are guided by the ball groovefaces of the outer and inner joint members; and

a cage having circumferentially displaced windows to accommodate theballs therein;

wherein the first group of grooves of the outer and inner joint membersare configured to have a first contact angle between its ball and ballgroove, respectively, and the second group of grooves of the outer andinner joint members are configured to have a second contact anglebetween its ball and ball groove, respectively, and wherein the secondcontact angle is selected to have an angle larger than the first contactangle;

wherein the first group of grooves of the outer and inner joint membersare configured to have a first pitch circle diameter, and the secondgroup of grooves of the outer and inner joint members are configured tohave a second pitch circle diameter, and wherein the second pitch circlediameter is larger than the first pitch circle diameter;

wherein the balls received in the second group of grooves of the outerand inner joint members are smaller than the balls received in the firstgroup of grooves of the outer and inner joint members.

According to the principles and further embodiments of the invention,the number of the torque transfer balls is an even number (for example,six, eight, ten, etc,), and the first skew angle of the outer jointmember and the first skew angle of the inner joint member are selectedto be in the range between about 10 degree and about 20 degree, and thesecond skew angle of the outer joint member and the second skew angle ofthe inner joint member are selected to be in the range between about 1degree and about 10 degree, more preferably between about 2 degree andabout 6 degree.

BRIEF DESCRIPTION OF THE DRAWINGS

The above described and other objects, features and advantages of thepresent invention will be more apparent from the presently preferredembodiments of the invention disclosed in the following description andillustrated in the accompanying drawings, in which:

FIG. 1( a) is a view illustrating a conventional cross groove joint withsix balls;

FIG. 1( b) is a cross-sectional view of the conventional cross groovejoint as shown in FIG. 1( a), taken along line A-A in the figure;

FIGS. 2( a)-2(c) are, respectively, a view of a conventional crossgroove joint with six balls, a partial side view thereof forillustrating the shapes of the ball grooves in the outer and inner jointmembers and movements of the balls in the grooves, and a partial sideview for illustrating movements of the balls in the cage;

FIG. 3( a) is a view illustrating a conventional cross groove joint witheight balls;

FIG. 3( b) is a cross-sectional view of the conventional cross groovejoint as shown in FIG. 3( a), taken along line B-B in the figure;

FIGS. 4( a)-4(c) are, respectively, a view of a conventional crossgroove joint with eight balls, a partial side development (i.e.,deployed or radially projected) view thereof for illustrating the shapesof the ball grooves in the outer and inner joint members and movementsof the balls in the grooves, and a partial side view for illustratingmovements of the balls in the cage;

FIGS. 5( a)-5(c) are, respectively, a view of the cross groove typeconstant velocity joint with eight balls, constructed according to onepreferred embodiment of the present invention, a side cross-sectionaland development view (i.e., deployed or radially projected on a plane)of the outer joint member thereof, and a side cross-sectional anddevelopment view of the inner joint member thereof;

FIG. 6 is a view illustrating the outer joint member of the cross groovetype constant velocity joint with eight balls, together with sectionalviews thereof taken in a radial direction and illustrating its grooveshapes, constructed according to another preferred embodiment of thepresent invention;

FIG. 7 is a view illustrating the inner joint member of the cross groovetype constant velocity joint with eight balls, together with sectionalviews thereof taken in a radial direction and illustrating its grooveshapes, which is to couple with the outer joint member of FIG. 6;

FIGS. 8( a)-8(b) are a cross-sectional view illustrating the grooveshapes of the first group of grooves, and a cross-sectional viewillustrating the groove shapes of the second group of grooves of thecross groove type constant velocity joint of FIGS. 6-7;

FIG. 9 is a view illustrating the outer joint member of the cross groovetype constant velocity joint with eight balls, together with sectionalviews thereof taken in a radial direction and illustrating its grooveshapes, constructed according to another preferred embodiment of thepresent invention;

FIG. 10 is a view illustrating the inner joint member of the crossgroove type constant velocity joint with eight balls, together withsectional views thereof taken in a radial direction and illustrating itsgroove shapes, which is to couple with the outer joint member of FIG. 9;and

FIGS. 11( a)-11(b) are a cross-sectional view illustrating the grooveshapes of the first group of grooves, and a cross-sectional viewillustrating the groove shapes of the second group of grooves of thecross groove type constant velocity joint of FIGS. 9-10.

DETAILED DESCRIPTION OF THE INVENTION

The present invention will be explained and illustrated below inassociation with several embodiments to be described later, inparticular, the cross groove joint of eight ball type. However, it isnoted that the present invention is not limited to the eight ball typejoint, but is applicable to the cross groove joint of any ball type, forexample, having six, eight, ten, or more balls.

Referring to FIGS. 5-11 of the drawings, the cross groove type constantvelocity joints of the present invention are described herein in detailsin association with several exemplary or preferred embodiments thereof.However, the following descriptions of such embodiments are intendedprimarily for illustrating the principles and exemplary constructions ofthe constant velocity joints of the present invention, and the presentinvention is not specifically limited to these exemplary embodiments.Thus, one skilled in the art can appreciate or recognize that variousmodifications and substitutions can be made thereto without departingfrom the spirit and scope of the present invention.

Throughout the description of the present application, common or similarelements are to be referred with the same or similar referencecharacters for simplicity purposes.

With reference to FIG. 5, one preferred embodiment of the presentinvention is described below in details. In this embodiment, the crossgroove joint includes an outer joint member 31 having a plurality of(i.e., eight) inwardly facing outer ball grooves 31 a-31 h, and an innerjoint member 33 placed inside the outer joint member 31 and having aplurality of (i.e., eight) outwardly facing inner ball grooves 33 a-33h. The corresponding outer and inner ball grooves 31 a-31 h and 33 a-33h face each other in pairs with each of the eight balls (not shown inFIG. 5) retained between each pair for torque transfer between the innerand outer joint members 31 and 33. The cross groove joint furtherincludes a cage (not shown in FIG. 5) containing eight cage windows (notshown in FIG. 5) for retaining the balls therein and to transmit therotational torque between the outer and inner joint members as issimilar to that shown in FIG. 4. However, unlike the conventional crossgroove joint as shown in FIG. 4, having the grooves alternately disposedin opposite directions with the same inclination angle δ, the ballgrooves 31 a-31 h and 33 a-33 h of the outer and inner joint membershave different groove shapes as shown in FIGS. 5( b) and 5(c).

More specifically, in the present embodiment the shapes of the ballgrooves are differentiated in two groups as illustrated in FIG. 5. Inparticular, a first group of grooves, namely, four ball grooves 31 a, 31c, 31 e, 31 g of the outer joint member 31 (displaced to each other withthe phase angle of 90 degree) and four ball grooves 33 a, 33 c, 33 e, 33g of the inner joint member 33 (displaced to each other with the phaseangle of 90 degree) each have a skewed groove with a first skew angle δ1throughout the length of the groove, but alternately arranged inopposite directions. On the other hand, a second group of grooves,namely, the remaining four ball grooves 31 b, 31 d, 31 f, 31 h of theouter joint member 31 and the remaining four ball grooves 33 b, 33 d, 33f, 33 h of the inner joint member 33 each have a skewed groove with asecond skew angle δ2 throughout the length of the groove, butalternately arranged in opposite directions. Here, the second skew angleδ2 is selected to have an angle less than the first skew angle δ1 whichis in turn selectable depending on the desired design of the jointsystem, and is generally the same as or similar to, and not exceeding,the skew angle of the conventional cross groove joint (as shown in FIG.4 for example). More specifically, according to one preferredembodiment, the first skew angle δ1 is selected to be in the rangebetween about 10 degree and about 20 degree, and the second skew angleδ2 is selected to be in the range between about 1 degree and about 10degree, more preferably between about 2 degree and about 6 degree. Withsuch a differentiated groove configuration, combined with one set ofgrooves of a bigger skew angle (similar to the conventional skew angle)and another set of grooves of a smaller skew angle, the minimumthickness (the least effective thickness) LL of the outer and innerjoint members 31 and 33 can be increased than that of the conventionalcross groove joint as shown in FIG. 4. As a result, the ball movementsin the cross groove joint and the size of cage windows can be reduceddue to the grooves of reduced skew angle, while enlarging the thicknessof cage webs as compared to that shown in FIG. 4. Accordingly, the crossgroove joint of the present embodiment can enhance the mechanicalstrength and durability of the joint as compared to the conventionaljoint.

As explained above, the above-described embodiment of FIG. 5 isadvantageous over the conventional cross groove joint. Moreparticularly, as the second group of grooves of the outer and innerjoint members 31 and 33 are configured to have a reduced skew angle δ2which is smaller than the first or regular skew angle δ1 of the firstgroup, the minimum thickness (the least effective thickness) LL of theouter and inner joint members 31 and 33 is increased, and thus, themechanical strength and durability of the joint is also improved overthe conventional joint.

However, as the grooves include two different skew angles, it may causea transmission irregularity or frictions due to the difference in therotational backlash in the first and second groove groups as the ballsreciprocate in the ball grooves. The rotational backlash occurs due tothe presence of clearances produced from the difference in dimensionbetween the ball and ball groove. As the first and second groove groupshave different skew angles, when the joint is operated and startstransferring the rotational torque in a reverse direction to cause theopposite sides of the groove surfaces to be in contact with the balls,the four ball grooves with bigger skew angle make the first contactswith the corresponding four balls, and then the remaining four ballgrooves with relatively smaller skew angle make the next contacts withthe remaining four balls, and thus, causing the difference in therotational backlash. This uneven or non-simultaneous contact may causeto decrease the durability of the joint, based on the possibility that aload is not distributed to all eight balls at the same time under thetorque, and thus, also to decrease a transmission efficiency of thejoint in operation.

In order to solve the above-identified potential drawbacks, theapplicants discovered that such rotational backlash can be decreased asthe contact angle between the ball and the ball groove for the inner andouter joint members increases and as the skew angle of the ball groovesincreases. The applicants further discovered that the rotationalbacklash can also be decreased as the pitch circle diameter (PCD)increases.

Based on these findings, the applicants further discovered severaleffective ways (as described below in details with reference to FIGS.6-11) to reduce the rotational backlash in the ball grooves, while alsomaintaining a similar or equivalent strength and durability of the jointas that of the previously described embodiment of FIG. 5.

With reference to FIGS. 6-8, one preferred embodiment of the presentinvention is described below in details. Except that described below,the basic structure of this joint is similar to that described shown inassociation with FIG. 5 above, and detailed descriptions regarding tothe common elements and structure of this embodiment are to be omittedherein for simplicity purposes, and to be referred above.

As is similar to the previous embodiment of FIG. 5, and unlike theconventional cross groove joint as shown in FIG. 4 (which has thegrooves alternately disposed in opposite directions with the sameinclination angle δ), the ball grooves 31 a-31 h and 33 a-33 h of theouter and inner joint members of the present embodiment havedifferentiated shapes or configurations as described below.

More specifically, in this embodiment as illustrated in FIGS. 6-8, afirst group of grooves, namely, four ball grooves 31 a, 31 c, 31 e, 31 gof the outer joint member 31 (displaced to each other with the phaseangle of 90 degree) and four ball grooves 33 a, 33 c, 33 e, 33 g of theinner joint member 33 (displaced to each other with the phase angle of90 degree) each have a skewed groove with a first skew angle β1throughout the length of the groove, in which the ball grooves in eachgroup are alternately arranged in opposite directions as shown. Inaddition, each groove of the first group is configured to have a firstcontact angle α1 between the ball and the ball groove as shown in FIGS.6, 7, and 8(a).

On the other hand, a second group of grooves, namely, the remaining fourball grooves 31 b, 31 d, 31 f, 31 h of the outer joint member 31 and theremaining four ball grooves 33 b, 33 d, 33 f, 33 h of the inner jointmember 33 each have a skewed groove with a second skew angle β2throughout the length of the groove, in which the ball grooves in eachgroup are alternately arranged in opposite directions as shown. Inaddition, each groove of the second group is configured to have a secondcontact angle α2 between the ball and the ball groove as shown in FIGS.6, 7, and 8(b).

In this embodiment, the second skew angle β2 is selected to have anangle less than the first skew angle β1 which is in turn selectabledepending on the desired design of the joint system, and is generallythe same as or similar to, and not exceeding, the skew angle of theconventional cross groove joint (as shown in FIG. 4 for example). Morespecifically, according to one preferred embodiment, the first skewangle β1 is selected to be in the range between about 10 degree andabout 20 degree, and the second skew angle β2 is selected to be in therange between about 1 degree and about 10 degree, more preferably,between about 2 degree and about 6 degree. Accordingly, as the outer andinner joint members include two different groove patterns, namely, witha first group of grooves of a bigger skew angle (similar to theconventional skew angle) and a second group of grooves of a smaller skewangle, the minimum thickness (the least effective thickness) LL of theouter and inner joint members 31 and 33 can be increased than that ofthe conventional cross groove joint as shown in FIG. 4. As a result, theball movements in the cross groove joint and the size of cage windowscan be reduced due to the grooves of reduced skew angle, while enlargingthe thickness of cage webs as compared to that shown in FIG. 4.Accordingly, the cross groove joint of the present embodiment canenhance the mechanical strength and durability of the joint as comparedto the conventional joint.

On the other hand, the second contact angle α2 is selected to have anangle larger than the first contact angle α1 which is in turn selectabledepending on the desired design of the joint system, and is generallythe same as or similar to the contact angle of the conventional crossgroove joint (as shown in FIG. 4 for example). More specifically,according to one preferred embodiment, the first contact angle α1 isselected to be in the range between about 30 degree and about 45 degree,and the second contact angle α2 is selected to be 1 to 10 degree largerthan the first contact angle α1, and thus, in the range between about 31degree and about 55 degree.

As explained above, the rotational backlash can be decreased as thecontact angle between the ball and the ball groove for the inner andouter joint members increases and as the skew angle of the ball groovesincreases. Therefore, in the present embodiment the increased rotationalbacklash in the second group of grooves due to the decrease of thesecond skew angle β2 is offset by the decreased rotational backlash dueto the increase of the second contact angle α2. Accordingly, thepotential risk of increasing the rotational backlash due to the decreaseof the second skew angle β2 (as may be occurring in the previousembodiment of FIG. 5, for example) is effectively resolved. Accordingly,the cross groove joint of the present embodiment can enhance themechanical strength and durability of the joint as compared to theconventional joint, while also resolving the potential risk of therotational backlash, and thus, reducing frictions and transmissionerrors in the joint causable by the rotational backlash when using twogroups of skewed grooves with different skew angles.

With reference to FIGS. 9-11, another preferred embodiment of thepresent invention is described below in details. The present embodimentincludes common or similar features as that of the previous embodimentas described above in connection with FIGS. 6-8. However, the outer andinner joint members of the present embodiment also include differentfeatures and/or further modifications and as described below.

More specifically, in this embodiment as illustrated in FIGS. 9-11, afirst group of grooves, namely, four ball grooves 31 a, 31 c, 31 e, 31 gof the outer joint member 31 (displaced to each other with the phaseangle of 90 degree) and four ball grooves 33 a, 33 c, 33 e, 33 g of theinner joint member 33 (displaced to each other with the phase angle of90 degree) each have a skewed groove with a first skew angle β1throughout the length of the groove, in which the ball grooves in eachgroup are alternately arranged in opposite directions as shown. Inaddition, each groove of the first group is configured to have a firstcontact angle α1 between the ball and the ball groove as shown in FIGS.9, 10, and 11(a). Moreover, the pitch circle diameter (PCD) defined bythe first group is configured to have a first pitch circle diameterPCD1.

On the other hand, a second group of grooves, namely, the remaining fourball grooves 31 b, 31 d, 31 f, 31 h of the outer joint member 31 and theremaining four ball grooves 33 b, 33 d, 33 f, 33 h of the inner jointmember 33 each have a skewed groove with a second skew angle β2throughout the length of the groove, in which the ball grooves in eachgroup are alternately arranged in opposite directions as shown. Inaddition, each groove of the second group is configured to have a secondcontact angle α2 between the ball and the ball groove as shown in FIGS.9, 10, and 11(b). Moreover, the pitch circle diameter (PCD) defined bythe second group is configured to have a second pitch circle diameterPCD2 which is larger than the first pitch circle diameter PCD1 of thefirst group, and the size of the balls in the second group is selectedto have a smaller dimension than the balls in the first group as shownin FIGS. 9-11.

In this embodiment, the second skew angle β2 is selected to have anangle less than the first skew angle β1 which is in turn selectabledepending on the desired design of the joint system, and is generallythe same as or similar to, and not exceeding, the skew angle of theconventional cross groove joint (as shown in FIG. 4 for example). Morespecifically, according to one preferred embodiment, the first skewangle β1 is selected to be in the range between about 10 degree andabout 20 degree, and the second skew angle β2 is selected to be in therange between about 1 degree and about 10 degree, more preferably,between about 2 degree and about 6 degree. Accordingly, as the outer andinner joint members include two different groove patterns, namely, witha first group of grooves of a bigger skew angle (similar to theconventional skew angle) and a second group of grooves of a smaller skewangle, the minimum thickness (the least effective thickness) LL of theouter and inner joint members 31 and 33 can be increased than that ofthe conventional cross groove joint as shown in FIG. 4. As a result, theball movements in the cross groove joint and the size of cage windowscan be reduced due to the grooves of reduced skew angle, while enlargingthe thickness of cage webs as compared to that shown in FIG. 4.Accordingly, the cross groove joint of the present embodiment canenhance the mechanical strength and durability of the joint as comparedto the conventional joint.

The second contact angle α2 is selected to have an angle larger than thefirst contact angle α1 which is in turn selectable depending on thedesired design of the joint system, and is generally the same as orsimilar to the contact angle of the conventional cross groove joint (asshown in FIG. 4 for example). More specifically, according to onepreferred embodiment, the first contact angle α1 is selected to be inthe range between about 30 degree and about 45 degree, and the secondcontact angle α2 is selected to be 1 to 10 degree larger than the firstcontact angle α1, and thus, in the range between about 31 degree andabout 55 degree.

In addition, as stated above, the second pitch circle diameter PCD2 isselected to have a larger dimension than the first pitch circle diameterPCD1 which is in turn selectable depending on the desired design of thejoint system, and is generally the same as or similar to the contactangle of the conventional cross groove joint. In addition, the size(ØD2) of the balls in the second group is selected to have a smallerdimension than the size (ØD1) of the balls in the first group as shownin FIGS. 9-11.

As explained above, the rotational backlash can be decreased as thecontact angle between the ball and the ball groove for the inner andouter joint members increases, as the skew angle of the ball groovesincreases, and also as the pitch circle diameter (PCD) increases.Therefore, in the present embodiment the increased rotational backlashin the second group of grooves due to the decrease of the second skewangle β2 is offset by the decreased rotational backlash due to theincrease of the second contact angle α2. Moreover, the increasedrotational backlash in the second group of grooves due to the decreaseof the second skew angle β2, can be further offset by the decreasedrotational backlash due to the increase of the second pitch circlediameter PCD2 and the reduced size of the balls in the second group.

Accordingly, the potential risk of increasing the rotational backlashdue to the decrease of the second skew angle β2 (as may be occurring inthe previous embodiment of FIG. 5) is effectively resolved. Accordingly,the cross groove joint of the present embodiment can enhance themechanical strength and durability of the joint as compared to theconventional joint, while also resolving the potential risk of therotational backlash, and thus, reducing frictions and transmissionerrors in the joint causable by the rotational backlash when using twogroups of skewed grooves with different skew angles.

As described above in connection with several exemplary embodimentsthereof, in order to provide an enhanced strength to the cage web andthe cross groove joint, the present invention provides a cross groovejoint including an outer joint member with a plurality of inwardlyfacing ball grooves and an inner joint member with a plurality ofoutwardly facing ball grooves, in which the shapes of the ball groovesof the outer and inner joint member are configured to increase thethickness and also the mechanical strength of the cage web as comparedto the conventional cross groove joint, in particular, by applyingdifferent skew angles to the ball grooves of the cross groove joint,namely, a regular skew angle to a first group and a reduced skew angleto a second group. Moreover, the potential risk of increasing rotationalbacklash is effectively resolved by applying differentiated or modifiedconfigurations in the shapes (e.g., the contact angle) of the secondgroup and/or the size of the pitch circle diameter and the ball size ofthe second group.

The above disclosed embodiments of the invention are representatives ofa presently preferred form of the invention, but are intended to beillustrative rather than definitive thereof. Accordingly, those skilledin the art will appreciate or recognize that various modifications andsubstitutions can be made thereto without departing from the spirit andscope of the present invention as set forth in the appended claims.

What is claimed is:
 1. A constant velocity joint for a drive systemcomprising: an outer joint member having a plurality of inwardly facingouter ball grooves, the outer ball grooves consisting of a first groupof grooves, each groove of which having a skewed groove shape with afirst skew angle (β1) other than zero and alternately arranged inopposite directions relative to an axis of rotation of outer jointmember, and a second group of grooves, each groove of which having askewed groove shape with a second skew angle (β2) other than zero andalternately arranged in opposite directions relative to an axis ofrotation of outer joint member, the second skew angle (β2) being lessthan the first skew angle (β1); an inner joint member disposed insidethe outer joint member and having a plurality of outwardly facing innerball grooves consisting of a first group of grooves, each groove ofwhich having a skewed groove shape with a first skew angle (β1) otherthan zero and alternately arranged in opposite directions relative to anaxis of rotation of inner joint member, and a second group of grooves,each groove of which having a skewed groove shape with a second skewangle (β1) (β2) other than zero and alternately arranged in oppositedirections relative to an axis of rotation of inner joint member, thesecond skew angle (β2) being less than the first skew angle (β1), eachinner ball groove of the inner joint member being coupled with acorresponding outer ball groove of the outer joint member generally incrossed pair; a plurality of torque transfer balls which are guided bythe ball groove faces of the outer and inner joint members; and a cagehaving circumferentially displaced windows to accommodate the ballstherein; wherein the first group of grooves of the outer and inner jointmembers are configured to have a first contact angle (α1) between itsball and ball groove, respectively, and the second group of grooves ofthe outer and inner joint members are configured to have a secondcontact angle (α2) between its ball and ball groove, respectively, andwherein the second contact angle (α2) is selected to have an anglelarger than the first contact angle (α1); wherein the first group ofgrooves of the outer and inner joint members are configured to have afirst pitch circle diameter (PCD1), and the second group of grooves ofthe outer and inner joint members are configured to have a second pitchcircle diameter (PCD2), and wherein the second pitch circle diameter(PCD2) is larger than the first pitch circle diameter (PCD1); whereinthe balls received in the second group of grooves of the outer and innerjoint members are smaller than the balls received in the first group ofgrooves of the outer and inner joint members.
 2. The constant velocityjoint of claim 1, wherein the number of the torque transfer balls is aneven number.
 3. The constant velocity joint of claim 1, wherein thefirst group of grooves of the outer and inner joint members,respectively, consist of four ball grooves displaced to one another witha phase angle of 90 degree, and the second group of grooves of the outerand inner joint members, respectively, consist of four ball groovesdisplaced to one another with a phase angle of 90 degree.
 4. Theconstant velocity joint of claim 1, wherein the first skew angle of theouter joint member and the first skew angle of the inner joint memberare selected to be in the range between about 10 degree and about 20degree, and the second skew angle of the outer joint member and thesecond skew angle of the inner joint member are selected to be in therange between about 1 degree and about 10 degree.
 5. The constantvelocity joint of claim 4, wherein the first contact angle of the outerjoint member and the first contact angle of the inner joint member areselected to be in the range between about 30 degree and about 45 degree,and the second contact angle of the outer joint member and the secondcontact angle of the inner joint member are selected to be 1 to 10degree larger than the first contact angle of the outer and inner jointmembers.